The present invention relates to an anisotropic film and a liquid crystal display using the same, and more specifically relates to an anisotropic film which can be used as a polarizing film of a liquid crystal display with maintaining the orientation of a polymerizable dichroic dye, and a liquid crystal display using the anisotropic film as a polarizing film.
In electron display, conventional CRT has come to be replaced with liquid crystal display (LCD) which is thin, light weight, and low electrical power consumption. In particular, plastic LCD in which a plastic film is used as a substrate in place of a glass substrate is characterized in that it is bendable, and capable of heterogeneous processing, but it is hardly cracked, besides the above characteristics. Therefore, plastic LCD is promising.
However, when an inexpensive polyethylene terephthalate film is used as the plastic substrate of plastic LCD, it is impossible to make the film substrate completely isotropic due to the properties of polyethylene terephthalate. If the substrate is not isotropic, undesirable phenomena, e.g., a leak of light, etc., occur in the liquid crystal display. For making the plastic film substrate completely isotropic, it is necessary to use expensive plastic materials.
The phenomenon of a light leak can be prevented by providing a polarizing film on the inside of the substrate of a liquid crystal display, but the thickness of a polarizing film is generally 200 xcexcor so, therefore it is substantially impossible to provide a polarizing film on the inside of the substrate.
Further, since a liquid crystal display has a visual angle characteristic, a liquid crystal display should be viewed within a limited visual angle for obtaining an image of the tone having no abnormality and high contrast. For improving the visual angle characteristic of a liquid crystal display, a liquid crystal display having a plurality of liquid crystal domains periodically different in the states of orientation of the liquid crystal and different in the visual angle characteristic of the liquid crystal in the same twist direction by 90xc2x0 has been supposed (disclosed in JP-A-7-5467 (the term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d)).
When a conventional polarizing film is used in a liquid crystal display having a plurality of liquid crystal domains different in the states of orientation, the polarizing axis of a polarizing film of every liquid crystal domain cannot be controlled. Accordingly, only the polarized light of the component which coincides with the polarizing axis direction of the detection side of the polarized lights passing the liquid crystal domain can be detected and a liquid crystal display having sufficient contrast cannot be obtained.
This problem results from the fact that conventional polarizing films cannot be patterned to the prescribed pattern. This is because it is extremely difficult with conventional polarizing films to arrange the part having a prescribed polarizing axis at the prescribed position of a film since conventional polarizing films are manufactured by the process of stretching high molecular films in the specific direction as a whole. Accordingly, it has been substantially impossible to arrange the part having a prescribed polarizing axis at the prescribed position of a liquid crystal display using conventional polarizing films.
An object of the present invention is to provide an anisotropic film which can be provided on the inside of the cell of a liquid crystal display as a polarizing film.
Another object of the present invention is to provide an anisotropic film functioning as a patterned polarizing film which makes it possible to arrange the part having a prescribed polarizing axis at the prescribed position of a liquid crystal display.
A further object of the present invention is to provide a liquid crystal display in which the above-described anisotropic film is provided on the inside of a liquid crystal cell.
The above objects of the present invention have been accomplished by the following means.
(1) An anisotropic film which is a hard film with maintaining the orientation of a polymerizable dichroic dye and forming a copolymer with other polymerizable monomer.
(2) The anisotropic film as described in the above item (1), wherein the hard film is formed by coating, on a substrate having been subjected to orientation, a solution containing a polymerizable dichroic dye, other polymerizable monomer and a polymerization initiator to orientate the polymerizable dichroic dye contained in the solution, and performing copolymerization reaction in the orientated state.
(3) The anisotropic film as described in the above item (2), wherein the coating solution contains in the ratio of from 50 to 95 wt % of a polymerizable dichroic dye, from 1 to 50 wt % of other polymerizable monomer, and from 0.5 to 5 wt % of a polymerization initiator (the components total up to 100 wt %).
(4) The anisotropic film as described in the above item (1), (2) or (3), which maintains the smectic state orientation of the polymerizable dichroic dye.
(5) The anisotropic film as described in the above item (1), (2) or (3), which maintains the smectic state orientation of the polymerizable dichroic dye.
(6) The anisotropic film as described in the above item (1), wherein the orientation direction of the polymerizable dichroic dye is maintained by patternization.
(7) A liquid crystal display, wherein the anisotropic film described in the above item (1) is provided on the inside of a cell as a polarizing film.
(8) A liquid crystal display, wherein the anisotropic film described in the above item (6) is provided at a cell as a polarizing film.
(9) The liquid crystal display as described in the above item (8), wherein the anisotropic film is provided on the inside of a cell.
The anisotropic film of the present invention is manufactured by orientating a dichroic dye in high order and fixing the dye while maintaining the orientation. Therefore, for example, even a thin layer having a thickness of 0.1 xcexcm or so can be made a polarizing film having high polarizing property. Conventional polarizing films were substantially incapable of being provided on the inside of the cells of liquid crystal displays due to their thickness of 200 xcexcm or so. However, the anisotropic film of the present invention can be provided on the inside of the cells, as a result, a liquid crystal display capable of ensuring sufficient light-shielding property and free of the problem of a leak of light can be obtained even when a plastic substrate is anisotropic.
When the anisotropic film of the present invention whose orientation direction is patternized and having a polarizing property, e.g., the anisotropic film which comprises domains shifting by 90xc2x0 in the direction of orientation formed alternately and periodically and having a polarizing property, is used as apolarizing film of a liquid crystal display, a liquid crystal display having a plurality of liquid crystal domains periodically different in the state of orientation of the liquid crystal and different in the visual angle characteristic of the liquid crystal in the same twist direction by 90xc2x0 can be easily obtained. Such a liquid crystal display exhibits excellent visual angle characteristic. In this case, the anisotropic film may be provided on the inside of a cell or may be provided on the outside of a substrate. It is of course preferred to provide an anisotropic film on the inside of a cell when the substrate is a plastic substrate.